Speaker Setup Changes for Different Amps?

I've been trying quite a few different amplifiers, preamps and integrateds and noticed that speakers "disappear" with some and not others but I can change the toe in and/or setup to make any of them disappear.  I don't know the science behind the way sounds emanates from speakers but does it make sense that one would need to tweak speaker positioning depending on the amp or preamp one is using? I suppose it's also possible that our ears just take time to get used to a sound (there's a word for this that I don't know) and short auditions or swaps are useless.